The invention relates to a method for mass simulation of motor vehicles on stationary test stands according to the preamble of the patent claim 1 as well as an apparatus for carrying out this method according to the preamble of the patent claim 5.
For stationary vehicle testing, roller test stands are predominantly used as stationary test stands. In this context, the drive wheels of a motor vehicle are coupled with the rollers of the test stand with respect to the rotational moment or torque. Since the vehicles do not move on these test stands, the inertial forces resulting from the acceleration of the vehicle mass must be simulated by the test stand, if the mass inertial moment of the test stand does not correspond with that of the vehicle mass. Hereby it is typical to simulate the difference of the inertial forces through a loading moment, which is generated, for example, by means of a direct current machine. The magnitude of the loading moment is regulated by a dynamic regulating circuit or closed control loop dependent on the respective acceleration.
For example, in order to exactly determine the exhaust gas properties of a vehicle determined on such test stands, the automobile industry and the environmental agencies place high demands on the measuring accuracy of such roller test stands. Therefore, all of the masses of the vehicle must be taken into consideration, which are not accelerated while driving on the test stand in comparison to driving on the street. These are, on the one hand, the translatory masses of the vehicle, such as the weight as well as the rotatable parts of the non-driven axles on the test stand.
In practice, these rotatable still-standing or non-moving masses were previously not exactly determined, but instead were approximately estimated based on empirical values. This was carried out because, although the weight of a vehicle is simple to determine, however it is not simple to determine the inertial moments of the rotating parts such as the wheels including the drive train, the clutch, the transmission and the like. Such a mass determination of these parts has previously been made more difficult, because frictional losses always additionally arise for these rotatable vehicle parts. For this reason, the sought-after inertia values have been approximately determined from the weight of the vehicle. Thus, from the vehicle weight, an increase or add-on of 3% to be added to the vehicle mass has been assumed for the rotatable vehicle parts. For a test stand run, that meant an increase or add-on of 1.5% onto the vehicle mass per non-rotating vehicle axle.
Such an estimation of the rotatable vehicle masses, which are not accelerated during the testing process on the test stand, can lead to an error of the mass simulation in unfavorable cases, whereby this error by itself already exceeds the required total measuring accuracy. Especially, this leads to considerable errors in the mass simulation if the distribution of the rotating inertias on the driven and non-driven axles is non-uniform.
Therefore, the invention is based on the object of improving the accuracy of the mass simulation on vehicle test stands.
This object has been achieved by the invention defined in the patent claims 1 and 5. Further developments and advantageous example embodiments of the invention are defined in the dependent claims.
The invention has the advantage that essentially all rotatable vehicle masses can be exactly determined by a measurement, and thereby consequent errors in the calculation of the driving resistances as well as of the mass simulation are avoidable.
The invention is described in further detail in connection with an example embodiment, which is illustrated in the drawing. The drawing shows a schematic illustration of a roller test stand with a regulating circuit or closed control loop 9, which contains an evaluation device 10 with a memory circuit 13 and a test input device 11, a junction point 8 and a regulator 12, and which regulates the direct current machine 1 corresponding to the vehicle mass that is to be simulated.
In the drawing, a direct current machine 1 is illustrated, which is rotatably connected with two testing stand rollers 6 via a connecting shaft 2. A vehicle 5 is schematically illustrated on the two test stand rollers 6, whereby the vehicle 5 is connected with one axle and the two vehicle wheels 4 in a force transmitting manner with the test stand rollers 6. Furthermore, the test stand rollers 6 are connected via the same shaft 2 with a rotational speed detection device, which is embodied as a tacho-generator 7. A rotational moment or torque pick-up 3, which is electrically connected with the regulating circuit 9, is arranged on the connecting shaft 2 between the direct current machine 1 and the test stand rollers 6 positioned opposite thereto. Thereby, the regulating circuit 9 consists of an evaluating device 10, onto which a memory circuit 13 and a test input device 11 are connected, a regulator 12 and a junction point 8. The tacho-generator 7 is connected with the evaluating device 10 on the input side. Furthermore, the junction point 8 is arranged between the regulator 12, the force pick-up 3, and the output of the evaluating device 10 and establishes an electrical connection therebetween. The regulator 12 provides a regulating signal via its output to the direct current machine 1. The direct current machine 1 can be operated both as a generator as well as a motor.
The test input device 11 connected with the evaluating device 10 contains two inputs for inputting a vehicle velocity v and the associated time t, and an output which supplies to the evaluating device 10 the delay xe2x88x92a determined from the inputs. The evaluating device 10 contains another input for inputting the translatory vehicle mass mF, which is inputtable as a previously known value. Moreover, the evaluating device 10 is still further connected with a memory circuit 13, which stores the test results determined on the test stand, such as the test stand mass mp, the mass of the rotatable vehicle drive masses mRad h on the rear axle and the mass of the remaining rotatable vehicle mass mRad v on the non-driven front axle.
The above described apparatus operates according to the following method steps: In the testing of a vehicle 5 on a roller test stand, the drive axle of the vehicle 5 as the test sample drives, via its vehicle wheels 4, the test stand rollers 6. On the other hand, the test stand rollers 6 can also be driven via the direct current machine 1. This is carried out preferably when the non-driven wheels 4 of a vehicle axle are located on the test stand rollers 6. Thereby, the tacho-generator 7 and the direct current machine 1 are simultaneously moved along via the connecting shaft 2. Thereby the tacho-generator 7 generates a signal, which is proportional to the velocity v or the angular velocity xcfx89. In the above described known differentiating evaluating method, the accelerating vehicle force which acts on the test stand rollers 6 can be derived from the angular velocity signal xcfx89. On the other hand, during the motor operation of the direct current machine 1, the force effect expended for the acceleration of the rotatable vehicle masses can also be determined by the differentiation of the velocity signal v or xcfx89. Therefrom, by means of the evaluating device 10, the corresponding mass values such as the test stand mass mP, the mass mRrad h rotating with the drive axle, the mass mRad v that is rotatable with the non-driven front axle, are calculable.
For the simulation of all of the vehicle masses that are effective on the street, first all of these individual masses must be determined or calculated, in order to then determine their effect by means of a roll-out test on the street. Then, from these measurement results, a driving resistance characteristic curve or corresponding values can be fixed or determined, which serve for the simulation of the determined vehicle masses.
The invention was based on the recognition that the accuracy of the mass simulation can be considerably improved, if the vehicle total mass mgesamt is measurably determined, because this mass mgesamt ultimately is effective during street driving, and the exact knowledge of which is necessary for the evaluation of the roll-out tests and determination of the driving resistance characteristic curve. In this context, the total mass mgesamt of the vehicle 5 effective on the street is calculated to:
mgesamt=mFmRad v+mRad h
Therein the symbols mean:
mF=vehicle mass;
mRad v=the rotatable mass of the front axle;
mRad h=the rotatable mass of the rear axle.
The vehicle mass mF sim for the determination that is to be assumed for the simulation by the test stand results in that the drive parts (for example the rear drive mRad h) that are already rotating along on the roller test stand are subtracted from the total mass mgesamt. From that follows the mathematical correlation:
mFsim=mgesamtxe2x88x92mRad h=mF+mRad v.
Since the translatory vehicle mass mF is generally known as the weight, the rotatable vehicle masses of the non-accelerated vehicle parts must be determined by measuring techniques on the test stand. To achieve this, first the test stand mass mp without the vehicle is determined with the aid of the recording of the loss characteristic curve and is stored in the memory circuit 13. Next, the testing vehicle 5 is first placed onto the test stand roller 6 with the one vehicle axle, for example the non-driven front axle, and then in the testing operation the loss recording and the mass determination are carried out. From this value, first the difference relative to the previously determined test stand mass mp is formed, so that the sought-after mass mRad v and the losses FV Rad v are given therefrom for the preceding loss recording of the test stand rollers 6 without a vehicle. These values are transmitted into the memory circuit 13 and are there available for further interrogation or reading-out.
Thereafter, the vehicle 5 is placed with its drive wheels 4 of the rear axle onto the test stand rollers 6, and is subjected to a renewed testing process with a loss recording and mass determination. In this context once again, in the evaluating device 10, the difference relative to the preceding loss recording of the test stand rollers 6 without a vehicle 5 is formed, so that the sought-after mass mRad h and the losses FV Rad h are given therefrom. These values are once again loaded into the memory circuit 13 and there remain available for further calculations.
From the preceding testing processes, all of the measured values are available to the evaluating device 10, which are necessary for the calculation of the total mass mgesamt, so that this may be calculated and stored into the memory circuit 13.
Likewise, from the available measured values, the vehicle mass mF sim that is to be simulated is calculable according to the formula:
mF sim=mgesamtxe2x88x92mRad h=mF+mRad v.
In order to be able to simulate a velocity dependent driving cycle it is further necessary to record a driving resistance characteristic curve FWK, which is determined by means of roll-out tests or experiments on the street. Such a roll-out test can also be carried out on the test stand before the vehicle testing, which in practice is generally the case.
In such a roll-out test or experiment, the test vehicle 5 is accelerated to a prescribed velocity or speed v on the street and then for its roll-out distance without drive, the velocity variation (xcex94v) per time unit (xcex94t) is determined. In this context, the velocity values v are sampled at certain time spacings or intervals t, and provided to the test input device 11. From these values, the test input device 11 calculates the roll-out characteristic xe2x88x92a over a prescribed velocity range, which corresponds to the real or actual driving resistance characteristic progression on the street. The determined roll-out characteristic xe2x88x92a of the vehicle 5 is provided to the evaluating device 10. According to the mathematical interrelation,             F      FWK        =                  -                  m          gesamt                    ·                        Δ          ⁢                      xe2x80x83                    ⁢          v                          Δ          ⁢                      xe2x80x83                    ⁢          t                      ,
the forces FFWK that are to be formed or determined are calculated from the available measuring results over the velocity by the evaluating device 10, which forces are prescribed as a nominal value to the regulating circuit 9 for controlling a prescribed driving path or distance simulation. From this, the difference force is determined, with the aid of the actual value Fist that is determined by the force pick-up 3, whereby this difference force is regulated-out or compensated by the regulator 12 for the mass simulation.